It is known to provide a loose-fitting plastic liner to extend the life of an existing low pressure pipeline. (By "low pressure" it is meant that pressures inside the pipeline do not exceed about 150 pounds per square inch ["psi"] when the pipeline is in service.) However, plastic liners are not used in high pressure pipelines such as water injection lines where pressures of 5,000 psi or more may be encountered inside the pipeline. The reason for this is that in conventional "relining" applications, the existing pipeline is used simply as a "guide" to receive a loose-fitting tubular plastic insert. The loose-fitting insert, once installed in the pipeline, serves as a new "pipeline"--the insert conveys the material formerly conveyed by the pipeline, but, in so doing, must be capable of withstanding whatever pressures may be required to transport the material there-through. Such loose-fitting plastic inserts are unsuitable for use in high pressure pipelines because they are not capable of withstanding the strain encountered when the interior region of the liner is pressurized, forcing the liner to expand radially toward the internal walls of the pipeline. Viewed in this light, it becomes apparent that, strictly speaking, the use of a loose-fitting insert is not properly described as "pipeline relining" because the insert does not serve as a "liner" but serves instead as a new pipeline having a somewhat smaller outside diameter than the inside diameter of the existing pipeline, there being an annular gap between the outer wall of the plastic insert and the inner wall of the existing pipeline.
The present invention, by contrast, provides a close-fitting liner. After completion of the procedure hereinafter described, the liner is disposed inside the pipeline with no annular gap between the liner and the pipeline. Because the liner contacts the inner walls of the pipeline, the liner itself need not be capable of withstanding the pressures encountered inside the pipeline.
Loose-fitting plastic inserts are conventionally installed in pipelines in an effort to extend the piping system life at a cost somewhat lower than that of installing a new pipeline. Loose-fitting plastic inserts are sometimes also intended to protect an existing pipeline against internal corrosion or abrasion. The installation of a loose-fitting plastic insert into a pipeline may also improve the flow characteristics of the pipeline beyond those observed in a similar pipeline which is not equipped with a loose-fitting plastic insert. Loose-fitting plastic inserts may also eliminate, or at least reduce the need to use oxygen scavengers, rust inhibitors or other chemicals to maintain the pipeline. The present invention, while providing these and other advantages, provides the further advantage that it is not restricted to use in low pressure applications but may be used in applications where internal pipeline pressures of several thousand psi are encountered.
Accordingly, it is an object of the present invention to provide a method of lining a pipeline with a plastic liner such that the lined pipeline is capable of withstanding internal pressures in excess of those which the liner alone could withstand.
A further object is to provide such a method which is relatively inexpensive, when compared with the cost of installing a new pipeline, and which is relatively easy to implement.